Colloquia - Fall 2013
August 27
"Light Scattering and Localization in Optically Dense Ultracold Atomic Systems"
Dr. Igor Sokolov
St. Petersburg State Technical University
We theoretically consider near resonance scattering of light from an ultracold atomic gas. Primary focus is on two cases. In the first, we treat a dilute gas; this corresponds to the so-called weak localization regime. In this regime we study both incoherent and coherent transport of radiation. In the second, we go to the case of a dense atomic gas, when dipole-dipole interactions are important. This regime of densities corresponds to the case when each atom on the average is within the near field light scattering zone of the other atoms. Under these conditions, a phase transition in light transport, the Anderson transition, is expected to occur.
September 17
"X-ray Lasers - From A Dream To Reality"
Dr. Linda Young
Argonne National Lab
The first optical laser was created by Ted Maiman in May of 1960 at Hughes Rearch Laboratories. From that small-scale demonstration, lasers are now ubiquitous in society, as celebrated by Laser Fest 2010, which marked the laser's 50th anniversary. Within that timespan we also witnessed the birth of the world's first x-ray free electron laser, LCLS at SLAC, which produced coherent radiation at 1.5 Ã...ngstroms on April 20, 2009. LCLS is no ordinary laser; it employs a 1-kilometer linac to accelerate electrons up to the speed of light and a 100-m array of magnets to produce x-ray bursts containing gigawatts of power, a billionfold increase over that available from x-ray synchrotrons, the other research tool used by scientists interested in determining 3D-structure of materials at the atomic scale. In this lecture I will describe the birth of the machine, the first experiments that elucidated the response of matter to these powerful x-ray laser pulses, and the challenges ahead as the x-ray laser enthusiasts from around the globe race to fulfill its dream of imaging single biomolecules without the need to resort to crystallization.
October 22
"Nuclear Quantum Monte Carlo"
Dr. Bob Wiringa
Argonne National Lab
Ab-initio calculations of the structure of light nuclei, starting from "bare" two-nucleon interactions that fit NN scattering data, have become feasible over the last two decades using quantum Monte Carlo methods. Three-nucleon interactions and two-body electroweak current operators are important additional inputs. Present variational and Green's function Monte Carlo methods allow us to study nuclei up to A=12 with unprecedented accuracy. Properties we can evaluate include binding and excitation energies and the relative stability of neighboring nuclei. We can also study fine details like charge-independence-breaking and isospin-mixing, one- and two-nucleon densities in configuration and momentum space, electromagnetic moments and electroweak transitions, and nucleon-nucleus scattering. Overall, we have made great progress in understanding how complicated aspects of nuclear structure arise from the pairwise interactions between individual nucleons.
October 29
"The Art of Producing Bright X-Rays and Its Current Revolution"
Dr. Kwang-Je Kim
ANL & University of Chicago
After the great success of the third generation x-ray facilities employing undulators in low-emittance electron storage rings, the ring-based source is currently making another advance towards approaching the diffraction limit for x-ray wavelengths, hence improving the brightness by two orders of magnitudes and higher. Drastically higher x-ray brightness became feasible recently with the success of high-gain x-ray amplifier using the SLAC linac, in which the gain is so high that the initially incoherent undulator radiation is amplified to intense, quasi-coherent radiation known as the self-amplified spontaneous emission (SASE). It is hoped that the high intensity and the short pulse length of SASE will enable single shot imaging of complex bio-molecules before destroying them. Several high-gain x-ray FEL facilities are either in operation or under construction around the world. Vigorous R&D effort is underway towards improving the power and spectrum of high-gain x-ray amplifier. A hard FEL is also possible in oscillator configuration by employing an x-ray resonator formed by Bragg reflectors such as diamond crystals. An x-ray FEL oscillator (XFELO) will produce fully coherent, high spectral purity (meV), pico-second x-ray pulses with MHz repetition rate and storage-ring-like stability, capable 29the of solving, for example, the long standing problem of high-Tc superconductivity via IXS. An XFELO can be further stabilized by referencing its output to a narrow nuclear resonance such as 57Fe to produce x-ray spectral combs, allowing x-ray quantum optical techniques for fundamental physics and improving the length/frequency standards.
November 5
"Using Lasers to Create Antimatter Jet"
Dr. Hui Chen
Lawrence Livermore National Lab
High-flux jets of electron-positron antimatter with trillion degree temperatures have recently been produced at high-intensity laser facilities. These breakthrough experiments open up a novel area of experimental high-energy-density plasma astrophysics. This presentation will begin with a broad overview, followed by a summary of the experimental components and the unique characteristics of the antimatter jets as well as their applications for understanding some of the most energetic cosmic events such as gamma ray bursts.
November 19
"Can the sea quark angular momentum help with understanding the nucleon spin"
Dr. Andi Klein
Los Alamos National Lab
Our current understanding of the origin of the nucleon spin is still limited and we are puzzled by the fact that roughly 50% of the spin is not accounted for. One of the possible explanations for this spin puzzle of the nucleons could come from including contributions from the angular momentum of the sea quarks. I will discuss the current status, introduce the Drell-Yan process to study the sea quark behavior and will present a detailed description of a planned and approved experiment at Fermilab with a transversely polarized target.
December 3
Senior Thesis Presentations
"Understanding Neutrons in Deuterium by Analyzing Electron-Deuteron Scattering"
Andrew MacClintock
"Laser-Induced Fluorescence and Optical Emission Spectroscopy Used for Plasma Diagnostics"
Joseph Newton
"The Construction, Operation, and Application of Demonstrations: How to Most Effectively Use Them in the Classroom"
Laura Pattison